1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to antenna structures used in such wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks to radio frequency identification (RFID) systems to radio frequency radar systems. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, radio frequency (RF) wireless communication systems may operate in accordance with one or more standards including, but not limited to, RFID, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), WCDMA, local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), LTE, WiMAX, and/or variations thereof. As another example, infrared (IR) communication systems may operate in accordance with one or more standards including, but not limited to, IrDA (Infrared Data Association).
For an RF wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). The receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier, which is coupled to the antenna.
Since a wireless communication begins and ends with the antenna, a properly designed antenna structure is an important component of wireless communication devices. As is known, the antenna structure is designed to have a desired impedance (e.g., 50 Ohms) at an operating frequency, a desired bandwidth centered at the desired operating frequency, and a desired length (e.g., ¼ wavelength of the operating frequency for a monopole antenna). As is further known, the antenna structure may include a single monopole or dipole antenna, a diversity antenna structure, an antenna array having the same polarization, an antenna array having different polarization, and/or any number of other electro-magnetic properties.
Two-dimensional antennas are known to include a meandering pattern or a micro strip configuration. For efficient antenna operation, the length of an antenna should be ¼ wavelength for a monopole antenna and ½ wavelength for a dipole antenna, where the wavelength (λ)=c/f, where c is the speed of light and f is frequency. For example, a ¼ wavelength antenna at 900 MHz has a total length of approximately 8.3 centimeters (i.e., 0.25*(3×108 m/s)/(900×106 c/s)=0.25*33 cm, where m/s is meters per second and c/s is cycles per second). As another example, a ¼ wavelength antenna at 2400 MHz has a total length of approximately 3.1 cm (i.e., 0.25*(3×108 m/s)/(2.4×109 c/s)=0.25*12.5 cm).
While two-dimensional antennas provide reasonably antenna performance for many wireless communication devices, there are issues when the wireless communication devices require full duplex operation and/or multiple input and/or multiple output (e.g., single input multiple output, multiple input multiple output, multiple input single output) operation. For example, for full duplex wireless communications to work reasonably well, received RF signals must be isolated from transmitted RF signals (e.g., >20 dBm). One popular mechanism is to use an isolator. Another popular mechanism is to use duplexers.